South Korea announced yesterday that they will be launching an investigation into the reported leak of classified U.S. documents. The documents in question are said to include information related to the U.S.-South Korea alliance and were reportedly leaked from the Pentagon.

According to NBC News, South Korea’s defense ministry stated that they will be demanding “appropriate measures” from the U.S. following the leak. The ministry did not disclose what specific measures they will be seeking.

CNN-News18 reported that South Korea plans to seek “appropriate steps from the U.S. after verification” of the leaked documents. It is not yet clear when the verification process will be completed.

The leaked documents have put the U.S.-South Korea alliance in the spotlight. TIME magazine reported that the leak is likely to strain the already tense relationship between the two countries.

Radio Free Europe / Radio Liberty reported that South Korea has stated that a “significant” number of the leaked documents are fake. It is unclear how many of the documents are authentic and how many are fraudulent.

The Wall Street Journal noted that the investigation comes at a time when the U.S. and South Korea are already facing tensions over North Korea’s nuclear program. The U.S. has been pressing South Korea to increase its contributions to the cost of maintaining U.S. troops in the country, a long-standing point of contention between the two allies.

As of now, it remains to be seen what the investigation will uncover and what the consequences of the leak will be for the U.S.-South Korea alliance.